Many mobile devices, such as mobile phones and tablet computing devices, include cameras that may be operated by a user to capture still and/or video images. Because such mobile devices are typically designed to be relatively thin, it can be important to design the cameras or imaging system to be as thin as possible in order to maintain a low-profile mobile device. One of the limiting factors as to how thin a mobile camera, imaging system or device can be constructed is the camera, as traditional mobile device cameras have a number of optical elements, e.g., a lens assembly and image sensor.
As imaging devices have become thinner and resolution of the camera has improved, the number of pixels designed into the image sensors has increased and the pixel pitch as decreased. For example, some current image sensors used in thin imaging devices include a 1 μm pixel pitch. However, image sensors are being developed toward submicron pixels. Small pixels enable the imaging device to capture images having more resolution, but the lens system must be able to pass image information that is out to the Nyquist Sample rate of the image sensor. This can be difficult to achieve for pixels that are 1.5 μm or smaller, because as the pixels become smaller the Nyquist Sample rate increases and the image sensor is susceptible to increased noise.
One approach has been to use an ultra-high resolution lens assembly, having a narrow field-of-view (“FOV”) in imaging devices to focus a scene onto an imaging sensor having small pixels. However, aligning an image sensor with an ultra-high resolution lens can be extremely difficult. Minor translational (e.g., X, Y, and Z linear directions) and rotational (e.g., tilt such as pitch, yaw and roll) misalignments can impact the overall performance of the imaging device. For a thin imaging device an important step in minimizing alignment errors is to glue the lens assembly directly to the sensor assembly that includes the image sensor. The direct gluing of the image sensor to the sensor cover glass is difficult to do without causing alignment errors during the gluing process. Such alignment concerns include ensuring the image sensor is positioned at the focal plane of the lens system and is aligned perpendicular to the optical axis of the lens system and at the correct angle thereby avoiding misalignment created by tilt or roll in the focal plane. Therefore it is important to use active alignment methods, where the imaging device's performance is actively measured during manufacture.